1. Field of the Invention
This invention relates to a color image sensing system of the kind using a solid-state image sensor.
2. Description of the Related Art
Many of the image sensing systems of the kind using a solid-state image sensor such as a CCD, MOS or the like have been formed with a color mosaic filter, etc., arranged in front of a single image sensor.
For example, they are arranged as follows: Among the picture elements of the image sensor, every four mutually adjacent picture elements are grouped as one set. For each of these sets, green (G) filters are allotted to two obliquely adjacent ones of the picture elements, a red (R) filter to one of the rest and a blue (B) filter to the other (a G-check, R and B method). This filter allotment is repeated for all the picture elements of the image sensor. With the picture elements arranged in this manner, a luminance signal Y and color-difference signals R-Y and B-Y are composed from the outputs of the image sensor and formed into a color video signal.
In another known method, the filter colors to be allotted to each of the groups (sets) of four picture elements of the image sensor are arranged to be white (W), green (G), yellow (Ye) and cyan (Cy) or to be magenta (Mg), green (G), yellow (Ye) and cyan (Cy).
In forming, for example, a luminance signal in accordance with the above-stated conventional method, however, spurious resolution tends to be caused by the color of a picture-taking object or by the ratio of color components of illumination light because the signal is composed of the outputs of the picture elements corresponding to a plurality of color filters. Under such a condition, it is hardly possible to obtain an adequate resolution.
In the case of the above-stated G-check, R and B method, for example, no luminance output is obtainable from the picture elements corresponding to the G and B filters in taking a picture of a red object. Then, in the horizontal direction of the image sensor, the luminance output is obtainable only from one of every two picture elements. This is equivalent to a decrease in the sampling frequency and thus increases the possibility of spurious resolution. Other methods mentioned above also present the same problem.